Led display modules and methods for making the same

ABSTRACT

An LED display module is disclosed. The LED display module includes: an active matrix substrate including a plurality of control units; a plurality of pairs of solder bumps arranged in a matrix on the active matrix substrate by transfer printing; a plurality of LED chips including pairs of electrodes connected to the corresponding plurality of pairs of solder bumps and arranged in a matrix on the active matrix substrate by transfer printing; grid barriers formed on the active matrix substrate to isolate the plurality of LED chips into individual chip units; and a multi-color cell layer including a plurality of color cells and aligned with the active matrix substrate such that the plurality of color cells match the plurality of LED chips in a one-to-one relationship. The plurality of color cells include first color cells, second color cells, and third color cells disposed consecutively in one direction.

TECHNICAL FIELD

The present invention relates to LED display modules including LED chipsarranged in a matrix on an active matrix substrate, and morespecifically to LED display modules including LED chips arranged in amatrix on an active matrix substrate by transfer printing.

BACKGROUND

Full-color light emitting diode (LED) displays in which LEDs emittinglight at different wavelengths are grouped into pixels have beenproposed as potential replacements for displays using LEDs as backlightlight sources. Each pixel consists of red, green, and blue LEDs or red,green, blue, and white LEDs. In such an LED display, red, green, andblue LEDs are fabricated in packages and are mounted on a substrate.However, due to the large distances between the constituent LEDs of eachpixel, high-quality resolution is difficult to obtain. Pixels consistingof packages of LEDs are difficult to apply to micro-LED displays thathave recently received much attention. LED pixel units have also beenproposed in which red LEDs, green LEDs, and blue LEDs constituting onepixel are mounted in one package. In such an LED pixel unit, thedistance between the adjacent LEDs (i.e. sub-pixels) in one pixel issmall but the distance between the adjacent pixels is difficult toreduce. Further, light interference may occur between the red, green,and blue LEDs.

Thus, for the purpose of reducing the distance between pixels, anattempt has been made to fabricate an LED display module in which groupsof LED chips, each of which includes red LED, green LED, and blue LEDchips, are arrayed in a matrix on a substrate. It is, however, difficultto mount the LED chips at predetermined heights and intervals on themicrometer-sized substrate. Different heights and intervals between theLED chips mounted on the substrate deteriorate the color reproducibilityof the LED display module. Wire bonding is necessary for electricalconnection between electrode pads and the LED chips on the substrate butit takes at least tens to hundreds of hours to manufacture one product.

Particularly, in the course of mounting tens to hundreds of LED chips onthe substrate, there is a high possibility that some of the LED chipsmay not be accurately located at desired heights from the substrate atdesired positions on the substrate. In this case, a designed lightemitting pattern cannot be achieved, resulting in poor colorreproducibility. Further, the LED chips are required to emit light atvarious wavelengths and should be divided on the basis of wavelength.For example, the LED chips emitting light at different wavelengthsshould be divided into unit groups. Thereafter, the unit groups shouldbe arranged, making it troublesome and difficult to fabricate the LEDdisplay modules.

SUMMARY

The present invention has been made in an effort to solve at least theproblems noted above. In an aspect of the present disclosure, LEDdisplay modules including LED chips arranged in a matrix on an activematrix substrate by transfer printing are disclosed.

In another aspect of the present disclosure, techniques for minimizing adistance between pixels and/or a distance between LEDs in each pixel areprovided herein.

A method for fabricating an LED display module according to one aspectof the present disclosure includes: preparing an active matrix substrateincluding a plurality of control units; transferring a plurality ofpairs of solder bumps arranged in a matrix on a bump support to theactive matrix substrate by primary transfer printing while maintainingthe original matrix of the solder bumps; transferring a plurality of LEDchips arranged in a matrix on a chip support to the active matrixsubstrate by secondary transfer printing while maintaining the originalmatrix of the LED chips; forming grid barriers on the active matrixsubstrate on which the plurality of LED chips are arranged in a matrix,to isolate the plurality of LED chips into individual chip units; andmatching a plurality of color cells including first color cells, secondcolor cells, and third color cells disposed consecutively in onedirection to the plurality of LED chips.

According to one embodiment, the active matrix substrate may be preparedby a CMOS process to form a control circuit in which a plurality ofcontrol units are arranged in a matrix on a base substrate.

According to one embodiment, the primary transfer printing may includefeeding a bonding carrier through a gap between the bump support and apick-up roller and a gap between the active matrix substrate and aplacing roller.

According to one embodiment, the primary transfer printing may includeallowing a pick-up roller to pressurize one area of the bonding carrieragainst the bump support when the one area of the bonding carrier isinterposed between the bump support and the pick-up roller, to bond theplurality of solder bumps to the bonding carrier while maintaining theoriginal matrix of the solder bumps on the bump support.

According to one embodiment, the primary transfer printing may includeallowing a placing roller to pressurize the one area of the bondingcarrier to which the plurality of solder bumps are bonded against theactive matrix substrate when the one area of the bonding carrier isinterposed between the active matrix substrate and the placing roller,to transfer and attach the plurality of solder bumps to the activematrix substrate while maintaining the original matrix of the solderbumps.

According to one embodiment, the primary transfer printing may includeallowing a pick-up roller to pressurize one area of the bonding carrieragainst the bump support when the one area of the bonding carrier isinterposed between the bump support and the pick-up roller, to bond theplurality of pairs of solder bumps to the bonding carrier whilemaintaining the original matrix of the pairs of solder bumps on the bumpsupport.

According to one embodiment, the primary transfer printing may includeallowing a placing roller to pressurize the one area of the bondingcarrier to which the plurality of pairs of solder bumps are bondedagainst the active matrix substrate when the one area of the bondingcarrier is interposed between the active matrix substrate and theplacing roller, to transfer and attach the plurality of pairs of solderbumps to the active matrix substrate while maintaining the originalmatrix of the pairs of solder bumps.

According to one embodiment, the secondary transfer printing may includefeeding a bonding carrier through a gap between the chip support and apick-up roller and a gap between the active matrix substrate and aplacing roller.

According to one embodiment, the secondary transfer printing may includeallowing a pick-up roller to pressurize one area of the bonding carrieragainst the chip support when the one area of the bonding carrier isinterposed between the chip support and the pick-up roller, to bond theplurality of LED chips to the chip support while maintaining theoriginal matrix of the plurality of LED chips on the chip support.

According to one embodiment, the secondary transfer printing may includeallowing a placing roller to pressurize the one area of the bondingcarrier to which the plurality of LED chips are bonded against theactive matrix substrate when the one area of the bonding carrier isinterposed between the active matrix substrate and the placing rollerand pairs of electrodes of the LED chips face the corresponding pairs ofsolder bumps, to transfer and attach the plurality of LED chips to theactive matrix substrate while maintaining the original matrix of theplurality of LED chips.

According to one embodiment, the grid barriers may be formed by screenprinting with a black color material to isolate the chips.

According to one embodiment, the color cell matching may include:forming a single multi-color cell layer in which the plurality of colorcells are arranged in a matrix; and matching the LED chips arranged in amatrix on the active matrix substrate to the color cells in a one-to-onerelationship.

According to one embodiment, the color cell matching may include:forming a multi-color cell layer in which the plurality of color cellsare arranged in a matrix and spaces between the neighboring color cellsare filled with light blocking grids; and aligning the active matrixsubstrate with the multi-color cell layer.

According to one embodiment, the plurality of LED chips may be blue LEDchips, the first color cells may include quantum dots or a fluorescentmaterial through which blue light from the corresponding blue LED chipsis converted to red light, the second color cells may include quantumdots or a fluorescent material through which blue light from thecorresponding blue LED chips is converted to green light, and the thirdcolor cells may allow blue light from the corresponding blue LED chipsto pass therethrough without color change.

According to one embodiment, the third color cells may include a greenfluorescent material.

According to one embodiment, the plurality of LED chips may include UVLED chips, the first color cells may include quantum dots or afluorescent material through which UV light from the corresponding UVLED chips is converted to red light, the second color cells may includequantum dots or a fluorescent material through which UV light from thecorresponding UV LED chips is converted to green light, and the thirdcolor cells may include quantum dots or a fluorescent material throughwhich UV light from the corresponding UV LED chips is converted to bluelight.

A display module according to a further aspect of the present disclosuremay include: an active matrix substrate including a plurality of controlunits; a plurality of pairs of solder bumps arranged in a matrix on theactive matrix substrate by transfer printing; a plurality of LED chipsincluding pairs of electrodes connected to the corresponding pluralityof pairs of solder bumps and arranged in a matrix at a constant heighton the active matrix substrate by transfer printing; grid barriersformed on the active matrix substrate to isolate the plurality of LEDchips into individual chip units; and a multi-color cell layer includinga plurality of color cells and aligned with the active matrix substratesuch that the plurality of color cells match the plurality of LED chipsin a one-to-one relationship, wherein the plurality of color cellsinclude first color cells, second color cells, and third color cellsdisposed consecutively in one direction.

According to one embodiment, the plurality of LED chips may include blueLED chips, the first color cells may include quantum dots or afluorescent material through which blue light from the correspondingblue LED chips is converted to red light, the second color cells mayinclude quantum dots or a fluorescent material through which blue lightfrom the corresponding blue LED chips is converted to green light, andthe third color cells may allow blue light from the blue LED chips topass therethrough without color change.

According to one embodiment, the third color cells may include a greenfluorescent material.

According to one embodiment, the plurality of LED chips may includeultra violet (UV) LED chips, the first color cells include quantum dotsor a fluorescent material through which UV light from the correspondingUV LED chips is converted to red light, the second color cells mayinclude quantum dots or a fluorescent material through which UV lightfrom the corresponding UV LED chips is converted to green light, and thethird color cells may include quantum dots or a fluorescent materialthrough which UV light from the corresponding UV LED chips is convertedto blue light.

According to one embodiment, the multi-color cell layer may furtherinclude light blocking grids disposed to fill spaces between theneighboring color cells, and the overlying light blocking grids and theunderlying grid barriers are arranged to face each other.

A display module according to another aspect of the present disclosuremay include: an active matrix substrate including a plurality of controlunits; a plurality of pairs of solder bumps arranged in a matrix on theactive matrix substrate; a plurality of LED chips including pairs ofelectrodes connected to the corresponding plurality of pairs of solderbumps and arranged in a matrix at a constant height on the active matrixsubstrate; grid barriers formed on the active matrix substrate toisolate the plurality of LED chips into individual chip units; and amulti-color cell layer including a plurality of color cells and alignedwith the active matrix substrate such that the plurality of color cellsmatch the plurality of LED chips in a one-to-one relationship, whereinthe plurality of color cells include first color cells, second colorcells, and third color cells disposed consecutively in one direction.

According to a first embodiment of the present disclosure, the LEDdisplay modules may include LED chips arranged in a matrix on an activematrix substrate. According to the present invention, the LED chips arearranged in a matrix on the active matrix substrate by transferprinting.

According to an aspect of the present disclosure, the micrometer-sizedLED chips may be mounted in a matrix at a uniform height on the activematrix substrate. The arrangement and dimensions lead to a markedimprovement in the color reproducibility of the final LED displaymodules.

According to an aspect of the present disclosure, a plurality of solderbumps can be arranged on the active matrix substrate in an easy andprecise manner within a short time without requiring much labor.

According to an aspect of the present disclosure, the plurality of LEDchips are precisely mounted in a matrix on the active matrix substrateon which the solder bumps are precisely arrayed in a matrix. With thisarrangement, the solder bumps can be individually electrically connectedto the LED chips in a controllable manner. Particularly, in the courseof mounting tens to hundreds of LED chips on the substrate, there is ahigh possibility that some of the LED chips may not be accuratelylocated at desired heights from the substrate at desired positions onthe substrate. In this case, a designed light emitting pattern cannot beachieved, resulting in poor color reproducibility. Further, the LEDchips are required to emit light at various wavelengths and should bedivided on the basis of wavelength. For example, the LED chips emittinglight at different wavelengths should be divided into unit groups.Thereafter, the unit groups should be arranged, making it troublesomeand difficult to fabricate the LED display modules. In contrast,according to an aspect of the present disclosure, grid barriers andlight blocking grids disposed in a multi-color cell layer can provideperfect light isolation between pixels and between sub-pixels.

According to a second embodiment of the present disclosure, the LEDpixel unit may be provided to minimize the distance between pixels andthe distance between sub-pixels in each pixel when applied to an LEDdisplay. The applicability of the LED pixel unit can be extended to amicro-LED display. There is a limitation in reducing the size of pixelsto about 200 μm² in conventional LED displays. In contrast, according tothe second embodiment of the present disclosure, the pixel size of theLED pixel unit can be significantly reduced to about 100 μm² or less,making the LED pixel unit applicable to a UHD display. In addition,according to the second embodiment of the present disclosure, the LEDpixel unit may be constructed in a simple manner. Furthermore, lightinterference between constituent light emitting units of sub-pixels ofthe LED pixel unit can be substantially completely blocked.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects and advantages of the invention will becomeapparent and more readily appreciated from the following description ofthe embodiments, taken in conjunction with the accompanying drawings ofwhich:

FIG. 1 is a flow chart for schematically explaining a method forfabricating an LED display module according to a first embodiment of thepresent invention;

FIG. 2 is a plan view illustrating an active matrix substrate preparedin the method of FIG. 1;

FIG. 3 is a front view illustrating an active matrix substrate preparedin the method of FIG. 1;

FIG. 4 is a view for explaining primary transfer printing for arrangingpairs of solder bumps in a matrix on an active matrix substrate;

FIG. 5 is a plan view illustrating pairs of solder bumps arranged in amatrix on a substrate by primary transfer printing;

FIG. 6 is a view for explaining secondary transfer printing forarranging LED chips in a matrix on an active matrix substrate;

FIG. 7 is a plan view illustrating LED chips mounted in a matrix on anactive matrix substrate after secondary transfer printing;

FIG. 8 is a cross-sectional view illustrating an LED chip flip-chipbonded to an active matrix substrate after secondary transfer printing;

FIG. 9 is a plan view illustrating grid barriers formed on an activematrix substrate to isolate LED chips into individual chip units;

FIG. 10 is a plan view illustrating a multi-color cell layer including aplurality of color cells;

FIG. 11 is a cross-sectional view illustrating a multi-color cell layer;

FIG. 12 is a view for explaining matching a plurality of color cells toLED chips;

FIG. 13 is a plan view illustrating an LED display module fabricated bythe method illustrated in FIGS. 1 to 12;

FIG. 14 is a cross-sectional view illustrating an LED display modulefabricated by the method illustrated in FIGS. 1 to 12;

FIG. 15 is a plan view illustrating an LED pixel unit according to oneembodiment of the present disclosure;

FIG. 16 is a cross-sectional view taken along line I-I of FIG. 15;

FIG. 17 is a plan view illustrating a micro-LED display panel to whichthe LED pixel unit of FIG. 15 is applied;

FIG. 18 illustrates a method for constructing LED pixel units accordingto one embodiment of the present disclosure;

FIG. 19 specifically illustrates a procedure for the production offirst, second, and third light emitting units in the method of FIG. 18;

FIG. 20 illustrates a procedure for the formation of a color filterarray film and a wavelength converting element during production of thefirst, second, and third light emitting units;

FIG. 21 illustrates a procedure for the production of an LED waferduring production of the first, second, and third light emitting units;and

FIG. 22 illustrates a further procedure for the production of an LEDwafer.

DETAILED DESCRIPTION

Exemplary embodiments of the present invention will now be describedwith reference to the accompanying drawings.

First Embodiment

1. Fabrication of LED Display Module

FIG. 1 illustrates a method for fabricating an LED display moduleaccording to a first embodiment of the present invention. Referring toFIG. 1, the method essentially includes: (S1) preparation of an activematrix substrate; (S2) primary transfer printing for forming pairs ofsolder bumps arranged in a matrix on the active matrix substrate; (S3)secondary transfer printing for mounting LED chips emitting light of thesame wavelength in a matrix on the active matrix substrate; (S4)isolation of the LED chips mounted on the active matrix substrate intoindividual chip units; and (S5) matching of color cells including firstcolor cells, second color cells, and third color cells to the LED chips.

Preparation of Active Matrix Substrate (S1)

Referring to FIGS. 2 and 3, an active matrix substrate 100 formed with acontrol circuit is prepared on a base substrate 102, for example, by aCMOS process. The CMOS process can be carried out similarly to a generalTFT backplane process. The control circuit may include electrodepatterns to which micro-LED chips having a size of 100 μm or less areapplicable. The control circuit includes a plurality of control units104 arranged in a matrix to individually control a plurality of LEDchips connected to the electrode patterns. For example, a constantcurrent source may be applied to the control circuit to individuallycontrol a plurality of LED chips. A constant rectification source may beapplied to the control circuit to individually control a plurality ofLED chips. For example, the control circuit may function as a static ortime-resolved multiplex cathode driver, an on/off control driver or apulse width modulation (PWM) control driver.

Primary Transfer Printing (S2)

Referring to FIGS. 4 and 5, a plurality of solder bumps 200 a and 200 bare transferred to the upper surface of the active matrix substrate 100by primary transfer printing. The primary transfer printing allows thearrangement of the plurality of pairs of solder bumps 200 a and 200 b ina matrix on the upper surface of the active matrix substrate 100.Electrode patterns corresponding to electrodes of micro-LED chips havinga size of 100 μm or less are previously formed at a predetermined heighton the upper surface of the active matrix substrate 100. The electrodepatterns are omitted to avoid complexity. Each of the electrode patternsincludes a pair of electrode patterns corresponding to a pair of bumps.The “solder bumps” are sometimes called “bump balls” or “solder balls”before flip-chip bonding of LED chips. For convenience, the term “solderbumps” will be used throughout the entire specification.

The primary transfer printing (S2) includes transferring pairs of solderbumps 200 a and 200 b arranged in a matrix on a bump support 1 to theactive matrix substrate 100 by a roll-to-roll transfer printingtechnique while maintaining the original matrix of the solder bumps. Abonding carrier 2, a pick-up roller 3, and a placing roller 4 are usedfor primary transfer printing.

Just before the primary transfer printing (S2), a plurality of solderbumps 200 a and 200 b are arranged in a matrix on the bump support 1 andthe bump support 1 is spaced a distance from the active matrix substrate100. The pick-up roller 3 forms a gap with the bump support 1 and isarranged directly above the bump support 1. The placing roller 4 forms agap with the active matrix substrate 100 and is arranged directly abovethe active matrix substrate 100.

The bonding carrier 2 takes the form of a film. The bonding carrier 2 ismoved in one direction by transfer rollers 6 and 7 and sequentiallypasses through the gap between the bump support 1 and the pick-up roller3 and the gap between the active matrix substrate 100 and the placingroller 4.

When one area of the bonding carrier 2 is interposed between the bumpsupport 1 and the pick-up roller 3, the pick-up roller 3 rolls whilepressurizing the one area of the bonding carrier 2 against the bumpsupport 1. As a result, the solder bumps 200 a and 200 b are bonded tothe bonding carrier 2 while maintaining the original matrix of thesolder bumps 200 a and 200 b on the bump support 1. When the bondingcarrier 2 is further moved until the area of the bonding carrier 2 towhich the solder bumps 200 a and 200 b are bonded reaches the gapbetween the active matrix substrate 100 and the placing roller 4, theplacing roller 4 rolls while pressurizing the corresponding area of thebonding carrier 2 against the active matrix substrate 100. As a result,the solder bumps 200 a and 200 b are transferred and attached to theactive matrix substrate 100 while maintaining the original matrix of thesolder bumps 200 a and 200 b bonded to the bonding carrier 2. Here, theactive matrix substrate 100 is imparted with a higher adhesive strengththan the bonding carrier 2. Before attachment of the solder bumps 200 aand 200 b to the bonding carrier 2, the bonding carrier 2 may beprimarily exposed to light. The primary exposure reduces the adhesivestrength of the bonding carrier 2 section-wise. Before attachment of thesolder bumps 200 a and 200 b to the active matrix substrate 100, thebonding carrier 2 may be secondarily exposed to light. The secondaryexposure reduces the adhesive strength of the bonding carrier 2 as awhole. By the primary transfer printing (S2), the plurality of pairs ofsolder bumps 200 a and 200 b are arranged in a matrix on the activematrix substrate 100.

Secondary Transfer Printing (S3)

Referring to FIGS. 6 to 8, a plurality of LED chips 300 are transferredto the upper surface of the active matrix substrate 100 by secondarytransfer printing. As a result of the secondary transfer printing, theplurality of LED chips 300 are arranged in a matrix on the upper surfaceof the active matrix substrate 100. The plurality of LED chips 300 areconnected to the pairs of solder bumps 200 a and 200 b and areelectrically connected to the electrode patterns 101 a and 101 b formedon the upper surface of the active matrix substrate 100. Simultaneouslywith the secondary transfer printing, the solder bumps can be bonded tothe active matrix substrate 100 under heat and pressure. Alternatively,the solder bumps may be bonded to the active matrix substrate 100 underheat and pressure after the secondary transfer printing.

The secondary transfer printing (S3) includes transferring LED chips 300arranged in a matrix on a chip support 1′ to the active matrix substrate100 by a roll-to-roll transfer printing technique while maintaining theoriginal matrix of the LED chips 300. A bonding carrier 2′, a pick-uproller 3′, and a placing roller 4′ are used for secondary transferprinting.

Just before the secondary transfer printing (S3), a plurality of LEDchips 300 are arranged in a matrix on the chip support 1′ and the chipsupport 1′ is spaced a distance from the active matrix substrate 100.The pick-up roller 3′ forms a gap with the chip support 1′ and isarranged directly above the chip support 1′. The placing roller 4′ formsa gap with the active matrix substrate 100 and is arranged directlyabove the active matrix substrate 100.

The bonding carrier 2′ takes the form of a film. The bonding carrier 2′is moved in one direction by transfer rollers 6′ and 7′ and sequentiallypasses through the gap between the chip support 1′ and the pick-uproller 3′ and the gap between the active matrix substrate 100 and theplacing roller 4′.

When one area of the bonding carrier 2′ is interposed between the chipsupport 1′ and the pick-up roller 3′, the pick-up roller 3′ rolls whilepressurizing the one area of the bonding carrier 2′ against the chipsupport 1′. As a result, the LED chips 300 are bonded to the bondingcarrier 2′ while maintaining the original matrix of the LED chips 300 onthe chip support 1′. When the bonding carrier 2′ is further moved untilthe area of the bonding carrier 2′ to which the LED chips 300 are bondedreaches the gap between the active matrix substrate 100 and the placingroller 4′ and pairs of electrodes 301 a and 301 b of the LED chips 300face the corresponding pairs of solder bumps 200 a and 200 b, theplacing roller 4′ rolls while pressurizing the corresponding area of thebonding carrier 2′ against the active matrix substrate 100. As a result,the LED chips 300 are transferred and attached to the active matrixsubstrate 100 while maintaining the original matrix of the LED chips 300bonded to the bonding carrier 2′. Here, the active matrix substrate 100is imparted with a higher adhesive strength than the bonding carrier 2′.Before attachment of the LED chips 300 to the bonding carrier 2′, thebonding carrier 2′ may be primarily exposed to light. The primaryexposure reduces the adhesive strength of the bonding carrier 2′section-wise. Before attachment of the LED chips 300 to the activematrix substrate 100, the bonding carrier 2′ may be secondarily exposedto light. The secondary exposure reduces the adhesive strength of thebonding carrier 2′ as a whole. By the secondary transfer printing (S3),the plurality of LED chips 300 including the plurality of electrodelayers 301 a and 301 b connected to the pairs of solder bumps 200 a and200 b are arranged in a matrix on the active matrix substrate 100.

As well illustrated in FIG. 8, each of the LED chips 300 is made ofgallium nitride semiconductors emitting short wavelength light (forexample, blue light) and includes a transparent substrate 310 having twoopposite surfaces, i.e. an upper surface through which light is emittedand a lower surface on which semiconductors grow, and a first conductivesemiconductor layer 320, an active layer 330, and a second conductivesemiconductor layer 340 formed sequentially downward from the lowersurface of the transparent substrate 310. The transparent substrate 310may be made of sapphire. The first conductive semiconductor layer 320,the active layer 330, and the second conductive semiconductor layer 340may be gallium nitride semiconductor layers grown on the sapphiresubstrate 310. The first conductive semiconductor layer 320 may be ann-type semiconductor layer and the second conductive semiconductor layer340 may be a p-type semiconductor layer. The active layer 330 mayinclude multi-quantum wells. The first conductive semiconductor layer320 and the second conductive semiconductor layer 340 are stepped on thelower surface of the LED chip 300. A first conductive electrode 301 a isdisposed in an area of the first conductive semiconductor layer 320 onthe lower surface of the LED chip and a second conductive electrode 301b is disposed in an area of the second conductive semiconductor layer340 on the lower surface of the LED chip.

The active matrix substrate 100 includes a plurality of electrodepatterns arranged in a matrix. Each of the electrode patterns includes afirst electrode pad 101 a and a second electrode pad 101 b. The pairs ofsolder bumps include a first solder bump 200 a and a second solder bump200 b. The first solder bump 200 a connects the first conductiveelectrode 301 a of the LED chip 300 to the first electrode pad 101 a ofthe active matrix substrate 100 and the second solder bump 200 bconnects the second conductive electrode 301 b of the LED chip 300 tothe first electrode pad 101 a of the active matrix substrate 100. Theplurality of pairs of solder bumps 200 a and 200 b are arranged in amatrix so as to correspond to the matrix of the electrode patterns.Likewise, the plurality of LED chips 300 are arranged in a matrix so asto correspond to the matrix of the plurality of pairs of solder bumps200 a and 200 b. The plurality of LED chips 300 are preferably LED chipsemitting short wavelength light, more preferably blue LED chips emittingblue light, when power is applied thereto.

Chip Isolation (S4)

As illustrated in FIG. 9, grid barriers 500 are disposed on the activematrix substrate 100 on which the plurality of LED chips 300 arearranged in a matrix. The grid barriers isolate the plurality of LEDchips 300 in individual chip units. The grid barriers 500 are made of alight absorbing black material and form unit cell spaces 501 surroundingthe respective LED chips 300. The grid barriers 500 are provided toisolate the LED chips emitting light of different colors and may beformed by screen printing through a 3-dimensional shadow mask. The gridbarriers 500 include a plurality of widthwise walls 510 and a pluralityof lengthwise walls 520 orthogonal to the widthwise walls 510.

Color Cell Matching (S5)

Referring to FIGS. 10 to 12, a plurality of color cells 610, 620, and630 match the corresponding LED chips 300. In this embodiment, theplurality of color cells 610, 620, and 630 may include first color cells610 through which blue light from the corresponding LED chips 300 isconverted to red light, second color cells 620 through which blue lightfrom the corresponding LED chips 300 is converted to green light, andthird color cells 630 allow blue light from the corresponding LED chips300 to pass therethrough without color change.

A single multi-color cell layer 600 is formed in which the plurality ofcolor cells 610, 620, and 630 are arranged in a matrix. The use of thesingle multi-color cell layer 600 facilitates matching of the pluralityof color cells 610, 620, and 630 to the plurality of LED chips 300. Themulti-color cell layer 600 is preferably formed by screen printingthrough a shadow mask.

The multi-color cell layer 600 includes light blocking grids 601disposed to fill spaces between the neighboring color cells 610, 620,and 630, in addition to the color cells 610, 620, and 630 arranged in amatrix. The multi-color cell layer 600 has upper and lower surfacesparallel to each other. The upper and lower surfaces of the multi-colorcell layer 600 lie at the same level as those of the light blockinggrids 601. Color cell groups in which the color cells 610, 620, and 630are sequentially arranged in a matrix in the widthwise or lengthwisedirection are repeatedly arranged.

The color cell layer 600 including the light blocking grids 601 may beformed by screen printing with a light absorbing black color material.

In this embodiment, the first color cells 610 and the second color cells620 receive short wavelength light from the corresponding LED chips 300,convert the wavelength of the received light, and outputs thewavelength-converted light. Each of the first color cells 610 and thesecond color cells 620 includes a wavelength converting material, suchas quantum dots or a fluorescent material (or a phosphorescentmaterial). Quantum dots are materials that output light of differentwavelengths in response to changes in particle size. Quantum dots can beadvantageously used in the embodiment of the present invention. In thisembodiment, blue light emitted from the corresponding LED chips 300 isconverted to red light through the first color cells 610 and blue lightemitted from the corresponding LED chips 300 is converted to red lightthrough the second color cells 620 located adjacent to the first colorcells 610 in the widthwise direction. Meanwhile, blue light emitted fromthe corresponding LED chips 300 passes through the third color cells 630located adjacent to the second color cells 620 in the widthwisedirection without color change. To this end, the third color cells 630are formed using a transparent material without a wavelength convertingmaterial. The three consecutive LED chips 300 in the widthwise directioncan match the first color cell 610, the second color cell 620, and thethird color cell 630, respectively, to form one pixel.

There may be used a combination of the color cells including a redwavelength converting material (quantum dots or a fluorescent material),the color cells including a green wavelength converting material, andthe color cells including no transparent converting material matched tothe neighboring blue LED chips, as described above. Alternatively, acombination of the color cells including a red wavelength convertingmaterial (quantum dots or a fluorescent material), the color cellsincluding a green wavelength converting material, and the color cellsincluding a blue wavelength converting material matched to neighboringUV LED chips may be used.

As best illustrated in FIG. 12, the active matrix substrate 100 on whichthe LED chips 300 are mounted is aligned with the multi-color cell layer600 such that the LED chips 300 arranged in a matrix match the colorcells 610, 620, and 630 in an one-to-one relationship. The peripheralportions of the active matrix substrate 100 and the multi-color celllayer 600 are sealed. When the multi-color cell layer 600 is alignedsuch that the LED chips 300 arranged in a matrix match the color cells610, 620, and 630, the underlying grid barriers 500 disposed on theactive matrix substrate 100 and the overlying grids 601 disposed in themulti-color cell layer 600 are aligned to face each other.

2. Structure of the LED Display Module

As illustrated in FIGS. 13 and 14, the LED display module according tothe first embodiment of the present invention includes: an active matrixsubstrate 100 having a plurality of control units 104 arranged in amatrix; a plurality of pairs of solder bumps 200 a and 200 b arranged ina matrix on the active matrix substrate 100 by transfer printing so asto correspond to the plurality of control units 104; a plurality of LEDchips 300 arranged in a matrix on the active matrix substrate 100 bytransfer printing so as to be electrically connected to the plurality ofpairs of solder bumps 200 a and 200 b, individually controlled by theplurality of control units 104, and emitting light of primary colors ata blue or UV wavelength when power is applied thereto; and a pluralityof color cells 610, 620, and 630 matched to the plurality of LED chips300.

The plurality of color cells 610, 620, and 630 are arrangedconsecutively along the widthwise or lengthwise direction and includefirst color cells 610, second color cells 620, and third color cell 630s adapted to receive the light of primary colors and to emit first colorlight, second color light, and third color light, respectively. Theplurality of LED chips 300 may be blue LED chips. In this case, thefirst color cells 610 may include quantum dots or a fluorescent materialto convert blue light to red light and emit the red light, the secondcolor cells 620 may include quantum dots or a fluorescent material toconvert blue light to green light and emit the green light, and thethird color cells 630 may be formed using a transparent material to emitblue light without wavelength change. The third color cells 630 mayinclude a green fluorescent material.

The plurality of color cells 610, 620, and 630 may be formed into onelayer, that is, a multi-color cell layer 600. The color cells 610, 620,and 630 are arranged above the active matrix substrate 100 on which theplurality of LED chips 300 are mounted. The multi-color cell layer 600includes light blocking grids 601 to isolate the first color cells 610from the second color cells 620 and to isolate the second color cells620 from the third color cells 630. The light blocking grids 601 arearranged to face the grid barriers adapted to isolate the LED chips 300on the active matrix substrate 100. With this arrangement, theneighboring LED chip-color cell sets can be perfectly isolated from oneanother.

It is noted that unexplained structures of the LED display module arethe same as the structures of the parts explained in the method forfabricating the LED display module.

Second Embodiment

FIG. 15 is a plan view illustrating an LED pixel unit according to asecond embodiment of the present invention, FIG. 16 is a cross-sectionalview taken along line I-I of FIG. 15, and FIG. 17 is a plan viewillustrating a micro-LED display panel to which the LED pixel unit ofFIG. 15 is applied.

Referring to FIGS. 15 to 17, an LED pixel unit 1 according to a secondembodiment of the present invention includes a light shielding wall 100and first, second, and third light emitting units 200, 300, and 400.

The light shielding wall 100 includes upper and lower surfaces parallelto each other. A first vertical hole 101, a second vertical hole 102,and a third vertical hole 103 are formed in parallel to one another fromthe upper surface to the lower surface of light shielding wall 100. Thelight shielding wall 100 surrounds the side surfaces of the first,second, and third light emitting units 200, 300, and 400, each of whichhas a cuboid shape. Thus, the first vertical hole 101, the secondvertical hole 102, and the third vertical hole 103 are substantiallyquadrangular in cross section. Tapered holes may also be used instead ofthe vertical holes.

The first light emitting unit 200 is arranged to fill the first verticalhole 101. The first light emitting unit 200 includes a first colorfilter 230 arranged in the upper portion of the inner space of the firstvertical hole 101, a first LED chip 210 arranged at a vertical positionbelow the first color filter 230, and a first wavelength convertingelement 220 interposed between the first color filter 230 and the firstLED chip 210.

The second light emitting unit 300 is arranged to fill the secondvertical hole 102. The second light emitting unit 300 includes a secondcolor filter 330 arranged in the upper portion of the inner space of thesecond vertical hole 102, a second LED chip 310 arranged at a verticalposition below the second color filter 330, and a second wavelengthconverting element 320 interposed between the second color filter 330and the second LED chip 310.

The third light emitting unit 400 is arranged to fill the third verticalhole 103. The third light emitting unit 400 includes a third colorfilter 430 arranged in the upper portion of the inner space of the thirdvertical hole 103, a third LED chip 410 arranged at a vertical positionbelow the third color filter 430, and a third wavelength convertingelement 420 interposed between the third color filter 430 and the thirdLED chip 410.

The first LED chip 210, the second LED chip 310, and the third LED chip410 emit light of the same blue wavelength band. Each of the firstwavelength converting element 220, the second wavelength convertingelement 320, and the third wavelength converting element 420 includes ayellow fluorescent material. The first wavelength converting element220, the second wavelength converting element 320, and the thirdwavelength converting element 420 convert the wavelength of blue lightfrom the first LED chip 210, the second LED chip 310, and the third LEDchip 410, respectively, and mix the wavelength-converted light withnon-converted light to produce white light.

The first color filter 230 filters out only light at a first wavelength,i.e. red light, from the white light obtained by the combination of thefirst LED chip 210 and the first wavelength converting element 220. Thesecond color filter 330 filters out only light at a second wavelength,i.e. green light, from the white light obtained by the combination ofthe second LED chip 310 and the second wavelength converting element320. The third color filter 430 filters out only light at a thirdwavelength, i.e. blue light, from the white light obtained by thecombination of the third LED chip 410 and the third wavelengthconverting element 420. The first light emitting unit 200, the secondlight emitting unit 300, and the third light emitting unit 400 as unitchips of the LED pixel unit 1 constitute sub-pixels emitting red light,green light, and blue light, respectively, to form one pixel in an LEDdisplay panel.

According to the present embodiment, each of the first LED chip 210, thesecond LED chip 310, and the third LED chip 410 includes a lightemitting surface and a pad forming surface. The light emitting surfaceis in contact with the wavelength converting element 220, 320 or 420 andthe pad forming surface is exposed to the outside through the bottom ofthe vertical hole 101, 102 or 103 of the light shielding wall 100. Aswill be explained in detail below, the first LED chip 210, the secondLED chip 310, and the third LED chip 410 include first conductiveelectrode pads E1 and second conductive electrode pads E2 on the padforming surfaces located opposite to the light emitting surfaces incontact with the first, second, and third wavelength converting elements220, 320, and 420, respectively. The first LED chip 210, the second LEDchip 310, and the third LED chip 410 can be individually driven whenpower is supplied from the outside through the first conductiveelectrode pads E1, the second conductive electrode pads E2, and solderbumps (not illustrated) connected thereto. The first conductiveelectrode pads E1 and the second conductive electrode pads E2 protrudefrom the lower surface of the light shielding wall 100 so that they canbe easily connected to bumps (not illustrated) connected to electrodes(not illustrated) on an external substrate (not illustrated).

The first LED chip 210, the second LED chip 310, and the third LED chip410 include transparent semiconductor growth substrates 211, 311, and411 and first conductive semiconductor layers 212, 312, and 412, activelayers 213, 313, and 413, and second conductive semiconductor layers214, 314, and 414 grown on the semiconductor growth substrates 211, 311,and 411, respectively. The transparent semiconductor growth substrates211, 311, and 411 may be made of sapphire. The first conductivesemiconductor layers 212, 312, and 412, the active layers 213, 313, and413, and the second conductive semiconductor layers 214, 314, and 414may be gallium nitride semiconductor layers grown on the sapphiresubstrates 211, 311, and 411, respectively. The first conductivesemiconductor layers 212, 312, and 412 may be n-type semiconductorlayers and the second conductive semiconductor layers 214, 314, and 414may be p-type semiconductor layers. The active layers 213, 313, and 413may include multi-quantum wells.

The first color filter 230, the second color filter 330, and the thirdcolor filter 430 are accommodated in the first vertical hole 101, thesecond vertical hole 102, and the third vertical hole 103 of the lightshielding wall 100, respectively, and are in contact with the inner wallsurfaces of the light shielding wall 100. Thus, the first color filter230, the second color filter 330, and the third color filter 430 areisolated from one another. The first, second, and third wavelengthconverting elements 220, 320, and 420 and the transparent semiconductorgrowth substrates 211, 311, and 411 of the first, second, and third LEDchips 210, 310, and 410 are accommodated in the first vertical hole 101,the second vertical hole 102, and the third vertical hole 103 of thelight shielding wall 100, respectively, and are in contact with theinner wall surfaces of the light shielding wall 100. Thus, the first,second, and third wavelength converting elements 220, 320, and 420 areisolated from one another and the transparent semiconductor growthsubstrates 211, 311, and 411 are isolated from one another. Due to thisconstruction, red light, green light, and blue light can be emitted fromthe first, second, and third light emitting units 200, 300, and 400without being mixed in the light shielding wall 100, avoiding the needto employ complicated package structures or barriers. The lightshielding wall 100 may be formed by a black color body, as explainedbelow.

As mentioned above, it is preferred that at least portions of the sidesurfaces of the transparent semiconductor growth substrates 211, 311,and 411 are in contact with the inner side surfaces of the lightshielding wall 100 and the side surfaces of some or all of the firstconductive semiconductor layers 212, 312, and 412, the active layers213, 313, and 413, and the second conductive semiconductor layers 214,314, and 414 are exposed to the outside without contact with the lightshielding wall 100. The exposure of at least portions of the firstconductive semiconductor layers 212, 312, and 412, the active layers213, 313, and 413, and the second conductive semiconductor layers 214,314, and 414 from the light shielding wall 100 can minimize loss oflight resulting from the absorption of light by the light shielding wall100.

For uniform distribution of light, it is preferred that the uppersurfaces of the first color filter 230, the second color filter 330, andthe third color filter 430 lie at the same level as the upper surface ofthe light shielding wall. This can be achieved in an easy and simplemanner by a method for fabricating LED pixel units, which will beexplained in detail below. For uniform light distribution, it is alsopreferred that the first wavelength converting element 220, the secondwavelength converting element 320, and the third wavelength convertingelement 420 lie at the same level. This can also be achieved in an easyand simple manner by the following method for fabricating LED pixelunits.

As mentioned earlier, the first LED chip 210, the second LED chip 310,and the third LED chip 410 are preferably blue LED chips that emit bluelight at a wavelength of 400 to 480 nm when power is applied thereto.Each of the first wavelength converting element 220, the secondwavelength converting element 320, and the third wavelength convertingelement 420 is preferably a yellow fluorescent material. The first colorfilter 230, the second color filter 330, and the third color filter 430are preferably a red filter, a green filter, and a blue filter thatfilter out red light, green light, and red light from white light,respectively. The LED chips 210, 310, and 410 of the first lightemitting unit 200, the second light emitting unit 300, and the thirdlight emitting unit 400 are the same LED chips grown on the samesubstrate by the same process. The wavelength converting elements 220,320, and 420 are separated from one larger wavelength convertingelement. Therefore, the same white light is produced until the first,second, and third color filters 230, 330, and 430 are reached. Thefirst, second, and third color filters 230, 330, and 430 can filter outlight at particular wavelengths (i.e. red, green, and blue light) fromthe white light.

The LED pixel unit 1, together with other LED pixel units constructed bythe same process, is illustrated in FIG. 18. The LED pixel units arearranged in a matrix on a substrate, as illustrated in FIG. 18. Here,the first conductive electrode pads and the second conductive electrodepads disposed on the pad forming surfaces of the LED chips of the lightemitting units of the LED pixel units are flip-chip bonded to electrodesdisposed on the substrate for individual driving of the LED chipsthrough solder bumps.

Referring now to FIGS. 18 to 22, an explanation will be given concerninga method for fabricating LED pixel units.

FIG. 18 illustrates a method for constructing LED pixel units accordingto the present invention, FIG. 19 specifically illustrates a procedurefor the production of first, second, and third light emitting units inthe method of FIG. 18, FIG. 20 illustrates a procedure for the formationof a laminate structure of a color filter array film and a wavelengthconverting element during production of the first, second, and thirdlight emitting units, FIG. 21 illustrates a procedure for the productionof an LED wafer during production of the first, second, and third lightemitting units, and FIG. 22 illustrates a further procedure for theproduction of an LED wafer.

Referring first to FIG. 18, a method for constructing LED pixel unitsaccording to the present invention includes: producing first lightemitting units 200, second light emitting units 300, and third lightemitting units 400 (see FIG. 19); arraying the first light emittingunits 200, the second light emitting units 300, and the third lightemitting units 400 such that the first light emitting units 200, thesecond light emitting units 300, and the third light emitting units 400are spaced apart from one another and a first group G1 including thefirst three consecutive light emitting units 200, 300, and 400, a secondgroup G2 including the second three consecutive light emitting units200, 300, and 400, and a third group G3 including the last threeconsecutive light emitting units 200, 300, and 400 are spaced apart fromone another; forming a planar light shielding wall 100 to fill spacesbetween the first light emitting units 200, the second light emittingunits 300, and the third light emitting units 400 and spaces between thefirst group G1, the second group G2, and the third group G3; and cuttingthe light shielding wall 100 such that the first group G1, the secondgroup G2, and the third group G3 are separated from one another. Thecutting of the light shielding wall 100 gives a plurality of LED pixelunits 1 corresponding to the groups G1, G2, and G3.

The production of the first light emitting units 200, the second lightemitting units 300, and the third light emitting units 400 will beexplained in more detail with reference to FIG. 19. First, the firstlight emitting units 200, the second light emitting units 300, and thethird light emitting units 400 are arrayed on the planar surface of anarray support substrate SS such that the total heights of the firstlight emitting units 200, the second light emitting units 300, and thethird light emitting units 400 are the same, the heights of the first,second, and third LED chips are the same, the heights of the first,second, and third wavelength converting elements are the same, and theheights of the first, second, and third color filters are the same.

Spaces between the first light emitting units 200, the second lightemitting units 300, and the third light emitting units 400 arrayed onthe support substrate SS and spaces between the groups G1, G2, and G3including the first light emitting unit 200, the second light emittingunit 300, and the third light emitting unit 400 are filled with a blackcolor body material. Then, the black color body material is coagulatedto form the light shielding wall 100. The vertical holes formed in thelight shielding wall 100 are substantially quadrangular in cross sectionand are upwardly and downwardly open because the light shielding wall100 substantially surrounds the side surfaces of the light emittingunits 200, 300, and 400, each of which has a substantially cuboid shape.

The light shielding wall 100 is cut in such a manner that theneighboring groups are separated from one another but the light emittingunits in each group are not separated from one another. As a result, LEDpixel units 1 can be obtained in which light interference between thefirst, second, and third light emitting units 200, 300, and 400 in eachgroup G1, G2 or G3 is completely blocked by the light shielding wall100. The light shielding wall 100 is preferably cut by sawing with ablade B.

Referring again to FIG. 16, the first light emitting unit 200, thesecond light emitting unit 300, and the third light emitting unit 400 ofeach LED pixel unit 1 include a first LED chip 210, a second LED chip310, and a third LED chip 410, each of which includes an electrode padforming surface and a light emitting surface opposite to the electrodepad forming surface, a first wavelength converting element 220, a secondwavelength converting element 320, and a third wavelength convertingelement 420 formed on the light emitting surfaces of the first LED chip210, the second LED chip 310, and the third LED chip 410, and a firstcolor filter 230, a second color filter 330, and a third color filter430 laminated on the first wavelength converting element 220, the secondwavelength converting element 320, and the third wavelength convertingelement 420, respectively.

As explained before, the first LED chip 210, the second LED chip 310,and the third LED chip 410 emit blue light of the same wavelength, thefirst wavelength converting element 220, the second wavelengthconverting element 320, and the third wavelength converting element 420convert the wavelength of the blue light and mix thewavelength-converted light with non-converted light to produce whitelight. The first color filter 230, the second color filter 330, and thethird color filter 430 filter out light at different wavelengths fromthe white light.

Referring next to FIG. 19, the production of the first, second, andthird light emitting units will be explained.

As well illustrated in FIG. 19, the production of the first, second, andthird light emitting units includes: forming a color filter array filmFM in which a first color filter 230, a second color filter 330, and athird color filter 430 are consecutively and repeatedly arrangedtwo-dimensionally on a temporary substrate TS; forming a wavelengthconverting element WM over the color filter array film FM to form alaminate structure of the color filter array film FM and the wavelengthconverting element WM; producing an LED wafer LW including an electrodepad forming surface and a light emitting surface opposite to each other;stacking the laminate structure on the LED wafer LW such that thewavelength converting element WM is in contact with the light emittingsurface, to construct a light emitting plate LP; and cutting the lightemitting plate LP such that a first light emitting unit 200 includingthe first LED chip 210, the first wavelength converting element 220, andthe first color filter 230, a second light emitting unit 300 includingthe second LED chip 310, the second wavelength converting element 320,and the second color filter 330, and a third light emitting unit 400including the third LED chip 410, the third wavelength convertingelement 420, and the third color filter 430 are separated from oneanother. The light emitting plate LP is cut by dicing with a diamondblade DB.

The separation of the first LED chip 210, the second LED chip 310, andthe third LED chip 410 from one larger LED wafer LW by cutting the lightemitting plate LP explains the same luminescent properties (includingthe same wavelength) and the same height of the LED chips. Theseparation of the first color filter 230, the second color filter 330,and the third color filter 430 from one larger wavelength convertingelement WM by cutting the light emitting plate LP explains the samewavelength converting properties and the same height of the colorfilters. The first color filter 230, the second color filter 330, andthe third color filter 430 have the same height that corresponds to thethickness of the color filter array film.

The first light emitting unit 200, the second light emitting unit 300,and the third light emitting unit 400 are used for the construction ofLED pixel units, which have been explained with reference to FIG. 18.

The lamination of the color filter array film FM and the wavelengthconverting element WM in the production of the first, second, and thirdlight emitting units will be explained in more detail with reference toFIG. 20.

Referring to FIG. 20, the formation of the color filter array filmincludes: forming first color filters 230 at desired positions on thetemporary substrate TS through a 3D shadow mask SD1; forming secondcolor filters 330 at positions on the temporary substrate TS through a3D shadow mask SD2 other than the positions of the first color filters230 such that the second color filters 330 are adjacent to the firstcolor filters 230; and forming third color filters 430 at positions onthe temporary substrate TS through a 3D shadow mask SD3 other than thepositions of the first color filters 230 and the second color filters330 such that the third color filters 430 are adjacent to the secondcolor filters 330. The wavelength converting element WM is formed to auniform thickness over the color filter array film FM including thefirst color filters 230, the second color filters 330, and the thirdcolor filters 430. A 3D shadow mask SD4 may be used to form thewavelength converting element WM. For example, a fluorescent material orquantum dots for wavelength conversion may be deposited to a uniformthickness on the color filter array film FM through a 3D shadow mask SD4to form the wavelength converting element WM.

FIG. 21 illustrates a procedure for the production of the LED waferduring production of the first, second, and third light emitting units.

Referring to FIG. 21, the LED wafer is produced by the followingprocedure. First, a sapphire wafer 11 suitable for the growth of galliumnitride semiconductor layers is prepared. Next, a first conductivesemiconductor layer 12, an active layer 13, and a second conductivesemiconductor layer 14 are sequentially allowed to grow on the surfaceof the sapphire wafer 11. The first conductive semiconductor layer 12,the active layer 13, and the second conductive semiconductor layer 14are gallium nitride semiconductor layers. Then, the second conductivesemiconductor layer 14 and the active layer 13 are etched topredetermined depths such that areas of the first conductivesemiconductor layer 12 are exposed. First conductive electrode pads E1are disposed on the exposed areas of the first conductive semiconductorlayer 12. Second conductive electrode pads E2 are formed on the secondconductive semiconductor layer 14 so as to pair with the firstconductive electrode pads E1. As a result of the etching, the exposedareas of the first conductive semiconductor layer 12 are stepped withthe remaining areas of the second conductive semiconductor layer 14. Onesurface of the LED wafer on which the first and second conductiveelectrode pads E1 and E2 becomes an electrode pad forming surface andthe opposite surface thereof (that is, the lower surface of the sapphirewafer 11) becomes a light emitting surface on which wavelengthconverting elements are to be laminated, which have been explainedabove.

Referring back to FIG. 19, the laminate structure of the wavelengthconverting element WM and the filter array film FM is stacked on the LEDwafer LW such that the wavelength converting element WM is in directcontact with the lower surface of the sapphire wafer 11 of the LED waferLW. As explained above, the light emitting plate constructed by stackingthe laminate structure of the wavelength converting element WM and thecolor filter array film FM on the LED wafer LW is cut into the firstlight emitting units 200, the second light emitting units 300, and thesecond light emitting units 300. The first light emitting units 200, thesecond light emitting units 300, and the third light emitting units 400include the first color filters 230, the second color filters 330, andthe third color filters 430, respectively. Each of the first lightemitting units 200, the second light emitting units 300, and the thirdlight emitting units 400 includes the pair of electrode pads E1 and E2.

FIG. 22 illustrates a further procedure for the production of an LEDwafer.

Referring to FIG. 22, a first conductive semiconductor layer 12, anactive layer, and a second conductive semiconductor layer 14 as galliumnitride semiconductor layers are subsequently allowed to grow on thesurface of a sapphire wafer 11, as in the previous procedure for theproduction of an LED wafer. The second conductive semiconductor layer 14and the active layer 13 are etched to predetermined depths such thatareas of the first conductive semiconductor layer 12 are exposed, whichis also the same as in the previous procedure. Next, an electrodeforming support substrate ES is formed on one surface of the LED waferincluding the exposed areas of the first conductive semiconductor layer12 and the exposed surfaces of the second conductive semiconductor layer14. The electrode forming support substrate ES includes first conductivemembers VA connected to the exposed areas of the first conductivesemiconductor layer 12 and second conductive members VB connected to thesecond conductive semiconductor layer 14. Next, the sapphire wafer 11 ispeeled off. At this time, a laminate structure of a wavelengthconverting element WM and a color filter array film FM is stacked suchthat the wavelength converting element WM is in contact with the backsurface of the first conductive semiconductor layer 11 from which thesapphire wafer 11 has been removed.

As noted herein, the present disclosure has been illustrated withspecific examples described for the purpose of illustration only, andthus one skilled in the art may appreciate that other alternative and/orequivalent implementations may be substituted for the specific examplesshown and described herein without departing from the scope of thepresent disclosure. As such, the present disclosure is intended to coverany adaptations or variations of the examples and/or equivalents shownand described herein, without departing from the spirit and the scope ofthe present disclosure.

What is claimed is:
 1. A method for fabricating a display module, comprising: preparing an active matrix substrate comprising a plurality of control units; transferring a plurality of pairs of solder bumps arranged in a matrix on a bump support to the active matrix substrate by primary transfer printing while maintaining an original matrix of the solder bumps; transferring a plurality of light emitting diode (LED) chips arranged in a matrix on a chip support to the active matrix substrate by secondary transfer printing while maintaining an original matrix of the LED chips; forming grid barriers on the active matrix substrate on which the plurality of LED chips are arranged in a matrix, to isolate the plurality of LED chips into individual chip units; and matching a plurality of color cells comprising first color cells, second color cells, and third color cells disposed consecutively in one direction to the plurality of LED chips.
 2. The method according to claim 1, wherein the active matrix substrate is prepared by a CMOS process to form a control circuit in which a plurality of control units are arranged in a matrix on a base substrate.
 3. The method according to claim 1, wherein the primary transfer printing comprises feeding a bonding carrier through a gap between the bump support and a pick-up roller and a gap between the active matrix substrate and a placing roller.
 4. The method according to claim 1, wherein the primary transfer printing comprises allowing a pick-up roller to pressurize one area of the bonding carrier against the bump support when the one area of the bonding carrier is interposed between the bump support and the pick-up roller, to bond the plurality of solder bumps to the bonding carrier while maintaining the original matrix of the solder bumps on the bump support.
 5. The method according to claim 1, wherein the primary transfer printing comprises allowing a placing roller to pressurize the one area of the bonding carrier to which the plurality of solder bumps are bonded against the active matrix substrate when the one area of the bonding carrier is interposed between the active matrix substrate and the placing roller, to transfer and attach the plurality of solder bumps to the active matrix substrate while maintaining the original matrix of the solder bumps.
 6. The method according to claim 1, wherein the secondary transfer printing comprises feeding a bonding carrier through a gap between the chip support and a pick-up roller and a gap between the active matrix substrate and a placing roller.
 7. The method according to claim 1, wherein the secondary transfer printing comprises allowing a pick-up roller to pressurize one area of the bonding carrier against the chip support when the one area of the bonding carrier is interposed between the chip support and the pick-up roller, to bond the plurality of LED chips to the chip support while maintaining the original matrix of the plurality of LED chips on the chip support.
 8. The method according to claim 1, wherein the secondary transfer printing comprises allowing a placing roller to pressurize the one area of the bonding carrier to which the plurality of LED chips are bonded against the active matrix substrate when the one area of the bonding carrier is interposed between the active matrix substrate and the placing roller and pairs of electrodes of the LED chips face the corresponding pairs of solder bumps, to transfer and attach the plurality of LED chips to the active matrix substrate while maintaining the original matrix of the plurality of LED chips.
 9. The method according to claim 1, wherein the grid barriers are formed by screen printing with a black color material to isolate the chips.
 10. The method according to claim 1, wherein the color cell matching comprises: forming a single multi-color cell layer in which the plurality of color cells are arranged in a matrix; and matching the LED chips arranged in a matrix on the active matrix substrate to the color cells in a one-to-one relationship.
 11. The method according to claim 1, wherein the color cell matching comprises: forming a multi-color cell layer in which the plurality of color cells are arranged in a matrix and spaces between the neighboring color cells are filled with light blocking grids; and aligning the active matrix substrate with the multi-color cell layer.
 12. The method according to claim 1, wherein the plurality of LED chips are blue LED chips, the first color cells comprise quantum dots or a fluorescent material through which blue light from the corresponding blue LED chips is converted to red light, the second color cells comprise quantum dots or a fluorescent material through which blue light from the corresponding blue LED chips is converted to green light, and the third color cells allow blue light from the corresponding blue LED chips to pass therethrough without color change.
 13. The method according to claim 1, wherein the third color cells comprise a green fluorescent material.
 14. The method according to claim 1, wherein the plurality of LED chips are ultra violet (UV) LED chips, the first color cells comprise quantum dots or a fluorescent material through which UV light from the corresponding UV LED chips is converted to red light, the second color cells comprise quantum dots or a fluorescent material through which UV light from the corresponding UV LED chips is converted to green light, and the third color cells comprise quantum dots or a fluorescent material through which UV light from the corresponding UV LED chips is converted to blue light.
 15. A display module comprising: an active matrix substrate comprising a plurality of control units; a plurality of pairs of solder bumps arranged in a matrix on the active matrix substrate by transfer printing; a plurality of LED chips comprising pairs of electrodes connected to the corresponding plurality of pairs of solder bumps and arranged in a matrix at a constant height on the active matrix substrate by transfer printing; grid barriers formed on the active matrix substrate to isolate the plurality of LED chips into individual chip units; and a multi-color cell layer comprising a plurality of color cells and aligned with the active matrix substrate such that the plurality of color cells match the plurality of LED chips in a one-to-one relationship, wherein the plurality of color cells comprise first color cells, second color cells, and third color cells disposed consecutively in one direction.
 16. The display module according to claim 15, wherein the plurality of LED chips are blue LED chips, the first color cells comprise quantum dots or a fluorescent material through which blue light from the corresponding blue LED chips is converted to red light, the second color cells comprise quantum dots or a fluorescent material through which blue light from the corresponding blue LED chips is converted to green light, and the third color cells allow blue light from the blue LED chips to pass therethrough without color change.
 17. The display module according to claim 15, wherein the third color cells comprise a green fluorescent material.
 18. The display module according to claim 15, wherein the plurality of LED chips are UV LED chips, the first color cells comprise quantum dots or a fluorescent material through which UV light from the corresponding UV LED chips is converted to red light, the second color cells comprise quantum dots or a fluorescent material through which UV light from the corresponding UV LED chips is converted to green light, and the third color cells comprise quantum dots or a fluorescent material through which UV light from the corresponding UV LED chips is converted to blue light.
 19. The display module according to claim 15, wherein the multi-color cell layer further comprises light blocking grids disposed to fill spaces between the neighboring color cells, and the overlying light blocking grids and the underlying grid barriers are arranged to face each other.
 20. A display module comprising: an active matrix substrate comprising a plurality of control units; a plurality of pairs of solder bumps arranged in a matrix on the active matrix substrate; a plurality of LED chips comprising pairs of electrodes connected to the corresponding plurality of pairs of solder bumps and arranged in a matrix at a constant height on the active matrix substrate; grid barriers formed on the active matrix substrate to isolate the plurality of LED chips into individual chip units; and a multi-color cell layer comprising a plurality of color cells and aligned with the active matrix substrate such that the plurality of color cells match the plurality of LED chips in a one-to-one relationship, wherein the plurality of color cells comprise first color cells, second color cells, and third color cells disposed consecutively in one direction. 